Galvanometer movable coil support



l f 1948 4ME. MoRRow 21,439,576

GALVNOMETER novABL coILv SUPPORT Filed Aug. 20. 1945 Patented Apr. 13, 1948 A' UNITED-z STATES PATENT l QEFICE l u.GM?VANOME'H:R12vi4(fi;;ir.licoILsUrron'r` "Marvin'E. Morrow, Tulsa, Okla., assigner tofCentury Geophysical Corporation, ATulsa, Okla., `a

corporation of Delaware y Application August 20, 1945,4 Serial No. 611,647

`13 Claims.

` The present invention relates to Iimprovements in oscillograph galvanometers', such as-are used in seismograph oscillograph cameras and the like. In theseinstruments as many as 2.5 to 36 separate DArsonval type galvanometers Vare required to record the outputs of as many channels of amplifier on a single moving sheet of photographically sensitive paper or ilm.` Itis imperative that the separate galvanometers 'of the bank be of small size in order to accommodate the large number of units inthe limited space of the camera.` yIt ls also imperative that extremely high sensitivity be employed inthese units because of the fact that they are used a1- most exclusively in, iield `operations and the amount ofA power available for useful gain in the 'amplifiers is limited. Furthermore, all channels of recording must be identical in response and therefore, the design of the galvanometers must be such as to permit the exact matching of units in frequency, damping and sensitivity.

Because of the very small dimensions necessarily required for such galvanometers and their constituent parts, considerable diiculty is experienced normally in assembling the vibratory elements in their enclosing barrels and adjusting the several parts to attain the desired degree of matching of the units in their frequency, damping and sensitivity characteristics. This is particularly true in the case of high frequency galvanometers, having a high degree of electrical damping. To increase the maximum frequency and degree of damping. pole piece inserts are normally installed in the enclosing barrel in` order to reduce the air gap to the maximum degree and thereby increase the flux density. This, however, further increases the dfculties of construction and assembly of the galvanometer since it necessarily reduces the dimensions of those portions of the vibratory element and its anchoring members which are required to pass between the pole piece inserts when being introduced into the barrel.

Furthermore,in the prior art galvanometers,

once the assembly within-the barrel hasbeen completed, and the vibratory element connected to its anchoring members and locked in the barrel, the vibratory element cannot normally be removed without substantial damage thereto or Without at least substantially altering `the previous adjustments. This is because the anchoring members are normally so constructed as to require their removal from `the` barrel separately and apart from the vibratory element connected, thereto.

production.

` It has been found that the manyfadvantages of the barrel type galvanometer can best be attained if the galvanometer` assembly canbe set up, adjusted and tested `in` final form before being placed inside the barrel. This can bedone i only if the entire assembly, or the major portion thereof, can be inserted and withdrawn from the barrel at any time without affecting `its oper-l ation inthe least and with a minimum amount of adjustmentofthe vibratory element.` once it has been' inserted in the barrel.

Accordingly, it is a principal objectief this in- `ventiongto provide a galvanometer assembly, in-

struction, which is of small size and `high sen sitivity, and which is readily` adapted to `mass Another important objectis toy provide a galvanometer which is capable of being damped to a high degree by electrical means.

An additional object is to'provide a totally enf closed barrel-type galvanometer which lscompletely sealed against the entry of water and dust.

A morespecific object 4is the provision of a totally enclosed, barrelftype galvanometer having a novel form of anchoringmember forfrictionally locking an end ofthe vibratoryelement to the interior of the barrel.

Other and more specific objectsof this inven-` tion will appear from the following description and from the accompanying drawings in which- Fig. 1 is a sectionalelevation of a galvanometer assembly in accordance with one embodiment of this invention:

Fig. 2 is a sectional elevation of a galvanometerV assembly in accordance with another embodiment of this invention; and

Fig. 3 is a detail of the galvanometer of Fig..2 viewed alongline 3-3 of Fig. 2. i. A

Referring to the drawing andto Fig. 1 in particular, the numeral `Ill designatesa'l galvanometer barrel made of non-magnetic material such as brass. The external diameter of the upper portion or the barrel is slightly larger than that of the lower portion which fits snugly into a circular hole I I in the polepiece structure of the magnet assembly. The latter comprises the pole pieces l2 and I3, the Alnlco magnets `|4 and I5 the free end of a spring contact .26.

and the base plate I6. The pole pieces I2 and I3 and baseplate I6 are made of high permeability magnetic material such as soft iron. The upper pole piece assembly. as shown in Fig. 3 is made up of three pieces. the two magnetic pole pieces I2 and I3 and the intermediate strip 44 of nonmagnetic material. These three pieces are normally brazed together to form a rigid unit. after which holes II are bored to receive the several galvanometer units normally employed in instruments such as seismograph oscillograph cameras.

current conducting suspension fibers 20 and 2|.` Y `These fibers are looped through the central holes of the beads that form the end structure ofthe coil and are soldered. The lower suspension fiber 20 is soldered into an anchor screw 2.2 which forms an anchoring member for the lower end of the vibratory element. The shaft of screw l22 passes through the bore of an insulating bushing 23 which fitssnugly into the lower end of the barrel I and is provided with an annular shoulder 23a which rests against the lower end of the barrel. Screw 22 is anchored to-the endof the barrel by means of a lock nut 24 and a second nut 25 which is adapted to make electrical contact with The other end of the latter is supported on an L-shaped insulating block 21 which is mounted by attachment to the inner faces of pole piece I2 and magnet I5 at their juncture. The two ends of coil I8 are ,brought out and connected at I1 and I'Ia to the respective suspension fibers 2li and! I. A current lead 2Gb is connected to contact 26 and a. ground lead 21b is connected to a. binding screw 21a which extends through insulating block 21 and into pole piece I2.

The upper end of suspension fiber 2I is formed into a loop and soldered to the bail 3 la of a coil spring 3| which is suspended from a square block 33, Block 33 is adapted to slide in square ways 33a formed in the upper portion of barrel I0 below an internally threaded section 35 of the barrel.

vA. set screw 32 is mounted in the side of barrel I0 driver or other suitable tool when it is desired to Y turn screw 34. A cap screw 36 having a wrench square 36a inthe top thereof is inserted in the threaded portion 35 of the barrel above the screw A mirror 23 is cemented to theupper suspension fiber 2| just above coil I8 and serves to indicate the vibratory motion of the coil. A window 30 is set in an opening in the side of barrel III to admit light from a conventional galvanometer lamp to the miror and to transmit the reected light to the film or sensitized paper in the usual manner.' Mirror 3011s preferably set 'at an angle to prevent reections from its outer surface from reaching the lm or senitized paper.

With the parts in the form described, the entire vibratory element.including coil I8, suspension fibers and 2 I, and mirror 23, together with the upper anchoring member, comprising screw 34, its connected block 33 and coil spring 3 I and the lower anchoring member, comprising screw 22, may be completely assembled .outside barrel I0 in a suitable jig or fixture and thoroughly tested and adjusted to the desired characteristicsv ing 23 is inserted in the lower end of barrel I0 in which it fitsy tightly. The entire vibratory element assembly described above is then inserted intothe barrel through the upper end, thereof.

f screw 34 engaging threads 35 and being screwed down therein until block 33 is engaged 'in ways 33a. The shaft of anchor screw 22 is passed through the bore vof insulating bushing 23 and nuts 24 and 25 applied to the end thereof to tightly anchor the vibratory element assembly to the lower portion of the barrel and to seal the same against the entry of moisture and dust. Coil I6 will then be properly positioned in the barrel between pole pieces I2 and I3, and mirror 23 will come opposite window 30. Screw 34 willthen be turned to adjust bloek`33 at a position along ways 33a to apply the desired degree of tension to the vibratory element. r Set screw 32 will then be tightened to lock block 33 in the adjusted posi-' n the entire vibratory element and its anchoring members may be inserted as a unit and the only adjustment required after installation of the unit in the barrel will be the longitudinal adjustment of block 33 to apply the desired degree of tension tothe vibratory element. This desired degree of tension may even be predetermined at the time the structure is assembledbefore installation in the barrel, so that it is only necessary to acust block 33 to an indicated' position in the ways 33a` which'will produce the pre-determined'degree of tension to the vibratory element. The assembly will be entirely sealed against entry of dirt, dust and moisture and is readily adapted for the use of an atmosphere of inert gas inside the barrel if desired.

Fig. 2 illustrates another embodiment in accordance with this invention which is particularly adapted for the manufacture of highA frequency galvanometers. This is accomplished by installing pole piece inserts in the barrel opposite the pole pieces, to thereby reduce the air gap and increase the flux density which permits a high degree of electrical damping of the coil. The coil dimensions may then be greatly reduced lto produce a vibratory element of as high a frequency as desired. However, the use of pole piece inserts constricts the bore of the barrel and the constriction may be of such degree in the case of high frequency galvanometers as to prevent the passage of the lower anchoring member through thel barrel, unless its lateral dimensions are reduced .to a degree which will weaken it too greatly for maintaining the desired degree of tension on the vibratory element.

Fig. 2 illustrates an embodiment which overcomes these disadvantages in the construction of a. high frequency galvanometer. In this embodiment pole piece inserts 3'I-3I'are inserted in barrel III opposite pole pieces I2 and I3 and in tight frictional contact therewith. The

`the identical parts bear the same identifying numerals in both figures.

The modified form of the lower anchoring member comprises a screw 38 having a smooth, downwardly tapering conical section 39 which I terminates in a straight, threaded shaft 40. An

insulatingbushing 4|, provided with an annular shoulder 42 adapted to bear against the end of barrel l is dimensioned to slip loosely into the lower end of vbarrel I0. The inner end portion of bushing 4I is providedwith a conical bore 43 having a taper substantially complementary to that of tapered section 39 of the screw 38 and the bore of the outer end portion of buslnng 4i is of substantially uniform diameter to accommodate threaded shaft 40.

In constructing a galvanometer employing pole-,piece inserts which are spaced too closely to permitv passage of the lower anchoring member therebetween. The assembly using the modified lower anchoring member is accomplished in the following manner:

, The entire vibratory element assembly is made up before installation in the barrel and completely tested and adjusted as previously described.

However. upper suspension fiber 2| is detachably connected to bail 31a of the upper anchoring member by looping the end of the ilber so that it may be hooked over the bail. The lower suspension :liber 2u is permanently soldered to the head of anchor screw 38. After the assembly is tested and adjusted as desired, the loop at the4 upper end of suspension ber 2 Iy is detached from bail 3| 'a and the remainder of the vibratory element assembly, comprising suspension fiber 2|, mirror 29, coil I8, lower suspension fiber 20 and anchor screw 38 are inserted into barrel l0 through the lower end thereof. This assembly is drawn through the barrel until the loop in suspension ber 2l appears at the upper end of the barrel, whereupon it is attached to bail 3Ia and is ordinarily soldered thereto. The assembly is then retracted through the barrel and screw 34 engaged with threads 35 and screwed down until threaded shaft 40 of screw 38 appears at the lower end of the barrel. Insulating bushing 4I is then slipped over the shaft end of screw 38 and inserted in the end of the barrel. Nuts 24 and 25 are then screwed on the threaded shaft and tightened. The tightening of nuts 24 and 25 draws conical section 39 of the screw into the tapered "bore of insulating bushing 4| and the resulting compression on the tapered bore of the bushing causes the bushing to expand laterally into tight frictional engagement with the inner wall' of barrel l0. This firmly locks the lower end of the vibratory element to the barrel and at the same time tightly seals the lower end of the barrel. Screw 34 is then adjusted in the manner previously described to apply the desired degree of tension to the vibratory element and set screw 32 tightened to x the position of block 33. Cap screw 38 is inserted in the upper eind of the barrel to complete the assembly. v

`It will be evident that the tapered form of 'anchoring member illustrated in Fig. 2 may be employed in place of anchor screw 22 and its complementary bushing 23' in a galvanometer of the form illustrated in Fig. 1 with equally satisfactory results. In such event, however, upper suspension ber 2| may be permanently connected to bail 31a before installation of the vibratory element in the barrel.

It will be recognized that various alterations and modifications may be made in the details of the structure herein described without departing from the scope of the appended claims but within the spirit of this invention.

What I claim and desire to secure by Letters Patent is:

l. A totally Aenclosed galvanometer of the barrel type, comprising a cylindrical barrel and a vibratory element mounted therein, said'vibratory element having an anchoring member connected to each end thereof adapted to form closures for the opposite ends of said barrel, said vibratory element and both of said anchoring members being insertable into said barrel through one end thereof in fully assembled form. and means for locking said anchoring members to opposite ends of said barrel. t

2. A totally enclosed galvanometer of the barrel type, comprising a cylindrical barrel and a vibratory element mounted therein, said vibratory element having an anchoring member connected to each end thereof adapted to form closures for the opposite ends of said barrel, said vibratory element and both lof said anchoring members being insertable into said barrel through one end thereof in fully assembled form, and

means' for locking said anchoring members to through one end thereof in, fully assembled form,

means for locking said anchoring members to opposite ends of said barrel, one of-said anchoring members having a tapered portion compressively engageable withits associated'locking means for expanding the latter into frictional engagement with the interior of said barrel, .and the other of said anchoring members having threadgd engagement with the opposite end of said arrel.

' 4. A totally enclosed galvanometer of the barvn'ected'. to each end thereof adapted to form closures for the opposite ends of said barrel, said vibratory element and both of said anchoring members being insertable into said barrel through one end thereof in fully assembled form, means for locking said anchoring members to opposite ends of said barrel, one of said anchoring members having a tapered portion compres- 4sively engageable with its associated locking means for expandinggthe latter into frictional engagement with the interior of said barrel, the other of said anchoring members having threaded engagement with the opposite end of said barrel and adjustable longitudinally therein, and supplemental means for locking said lastmentioned anchoring means in the adjusted position.

' 5. A totally enclosed galvanometer of the barrel type, comprising a. cylindrical barrel and a vibratory element mounted therein, said vibratory element having an anchoring member connected to each end thereof adapted to form closures for the opposite ends of said barrel, said vibratory element and both of said anchoring members being insertable into saidl barrel through one end thereof in fully assembled form, means for locking said anchoring members to opposite ends of said barrel, one of said anchoring members having a tapered portion compressively engageable with its associated locking means for expanding the latter into frictional engagement with the interior of said barrel, the other of said anchoring members having threaded engagement with the opposite end of said barrel, and an additional closure member for said opposite end of said barrel.

6. A totally enclosed galvanometer of the barrel type, comprising a cylindrical barrel and a vibratory element mounted therein, said vibratory element having a first anchoring member detachably connected to one end thereof and a second anchoring member permanently connected to the opposite end thereof, means for locking said second anchoring member to said barrel, and means carried by said second anchoring member and cooperating with said locking means to effect frictional engagement of said locking means with the interior of said barrel.

7. A totally enclosed galvanometer of the barrel type, comprising a cylindrical barrel and a vibratory element mounted therein, said vibratory element Ahaving a rst anchoring member detachably connected to one end thereof and a second anchoring member permanently connected to the opposite end thereof, means for locking said second anchoring member to said barrel, said second anchoring member having atapered portion compressively engageable with said locking means for expanding the latter into frictional engagement with the interior of said barrel.

8. A totally enclosed galvanometer of the barrel type, comprising a cylindrical barrel having an internally threaded portion at one end thereof, a vibratory element mounted in said barrel, rst and second anchoring members, said rst anchoring member being detachably connected with one end of said vibratory element and in threaded engagement with said threaded portion of said barrel, said second anchoring member being permanently connected to the opposite end of said vibratory element, means for locking said second anchoring member to said barrel, said means including a tapered member carried by said second anchoring member and compressively engageable with said locking means to expand the latter into frictional engagement with the interior of said barrel, and a supplemental closure member mounted in the outer end of said threaded portion of said barrel.

9. A totally enclosed galvanometer of the barrel type, comprising a cylindrical barrel having a constriction in an intermediate portion of the bore thereof, a first anchoring member mounted in the bore at one end of said barrel, a vibratory element mounted in the barrel and extending through said constricted portion, said vibratory element being detachably connected at one end to said first anchoring member, a second anchoring member permanently connected to the opposite end of said vibratory element and insertable therewith through the opposite end of said barrel, means for locking said second anchoring member to said barrel, and means carried by said second anchoring member and cooperating with said locking means to eiiect frictional engagement of said locking means with the interior of said barrel.

10. A totally \enclosed galvanometer orf the barrel type comprising, a cylindrical barrel having a. constriction in an intermediate portion 'of the bore thereof, a nrst anchoring member mounted in the bore at, one end of said barrel, a vibratory element mounted in the barrel and extending through said constriction, said vibratory element being detachably connected at one end to said first anchoring member, a second anchoring member permanently connected to the opposite end of said vibratory. elementv and insertable therewith through the opposite end of said barrel and means for locking said second anchoring member to said barrel, said second anchoring member having a tapered portion compressively engageable with said locking means for expanding the latter into frictional engagement with the interior of said barrel.

11. In a totally enclosed galvanometer of the barrel type which includes a cylindrical barrel having a constriction in an intermediate portion of the bore thereof and a vibratory element mounted in said barrel and extending through said constriction, means for anchoring said vibratory element to the opposite ends of said barrel comprising, a rst anchoring member mounted in one end of said barrel and detachably connected to one end of said vibratory element, a second anchoring member permanently connected to the opposite end of said vibratory element and insertable therewith through the opposite end of said barrel, means for locking said second anchoring member to the opposite end of said barrel, and means carried by said second anchoring member and cooperating with said locking means to effect frictional engagementv of said locking mean-s with the interior of said barrel.

12. In a totally enclosed galvanometer of the' barrel type, which includes a cylindrical barrel having a constriction in an intermediate portion of the bore thereof` and a vibratory elementmounted in said barrel and extending through said constriction, means for anchoring said vibratory element to the opposite ends of said barrel comprising, a rst -anchoring member mounted in one end of said barrel and detachably connected to one end of said vibratory element, a second anchoring member permanently connected to the opposite end of said vibratory element and insertableitherewith through the opposite end of said barrel, and means for locking said second anchoring member to the opposite end of said barrel, said second anchoring member having a tapered portion compressively engageable with said locking means for expanding the latter intov friction-al engagement with the interior of said barrel.

13. In a totally enclosed galvanometer of the barrel type, which includes a cylindrical barrel having a constriction in an intermediate portion of the bore thereof and a vibratory element mounted in the barrel and extending through said constriction, means for anchoring said vibratory element to the opposite ends of said barrel comprising a liirst anchoring member screwed into one end of the barrel and detachably 9 10 connected to one end of the vibrators element. and a second anchoring member permanently REFERENCES CITED connected 'bo the opposite end of said vlbrgtgry The .tlbllowm' references are of record inthe element and adapted to be anchored to the inme vof this Damit: tenor of the opposite end of said barrel by fric- 5 UNITED STATES PATENTS tional engagement therewith.

' Number Name I Date MARVIN E, MQRROW. 2,149,442 Knnmtine Mar. 7, 1939 2,389,081 Redmond Nov. 13,` 1945 

